Dealing with changing environmental conditions: dispersal and local adaptation in marine nematodes.

Type:

Master Thesis subject (30 ECTS)

programme:

EMBC+

Dealing with changing environmental conditions is an important characteristic for populations to survive. Organisms can cope with this in three different ways: by dispersing away, by phenotypic plasticity or by local adaptation.
Dispersal is the process in which organisms are moving away from their natal habitat. In this way they are capable of avoiding adverse environmental conditions and can distribute their genetic diversity beyond their local habitat. Marine environments are often seen as open systems, due to the high degree of dispersal in organisms and the absence of obvious barriers in the water. However nematodes, by far the most abundant and species-rich phylum in marine environments, and other meiofauna have low dispersal capacities caused by their small size, their restricted swimming abilities and their lack of pelagic stages. Nevertheless, many taxa have a seemingly cosmopolitan distribution. This contradiction is referred to as the meiofauna paradox. Research shows that dispersal in nematodes is more common than previously thought, with passive dispersal probably being dominant. As an example, organisms may raft on drifting macro-algae or be transported with the flows. Nematodes are not; however, merely passively dependent on dispersal, as they appear capable of actively entering the water column as well choosing preferred habitats for settling. Another part of the explanation for the meiofauna paradox is that a possible genetic diversity may be hidden behind the morphological similarity of many species. Such cryptic diversity has, for instance, been well documented in the marine nematode, Rhabditis (Pellioditis) marina.
Beside dispersal, another way of dealing with environmental changes is phenotypic plasticity, the collective term for changes in an individual’s behaviour, morphology and physiology induced by different environmental conditions. Such changes lead to a higher relative fitness in the local habitat and are considered local adaptations when they are supported by genetic changes at the population level. Cryptic species may have different environmental preferences and changing environmental conditions can affect the fitness of individual species and the interactions between them. Investigating this is important to predict persistence of local populations and community composition, which is extremely important in times of global change.
According to the interest of the student, the focus of the research can be on (1) both active and passive dispersal or (2) local adaptation in marine nematodes, with particular emphasis on different cryptic species, their (differential?) response to environmental changes, and the interactions between them.